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marți, 30 octombrie 2012

Revisiting Doomsday at the LHC

We are currently holed up in Boston, bracing ourselves for the wrath of Hurricane Sandy along with the rest of the Northeast, and kicking ourselves for not having the good sense to stay home in sunny Los Angeles. (But the Moving Naturalism Forward conference we attended was fantastic, whereby we learned a great deal about the nature of reality, emergence, morality, consciousness and free will from some very smart people — and were chuffed to discover that philosopher Daniel Dennett looks like an amiable intellectual Kris Kringle.)

But Sandy isn’t the only harbinger of disaster; this is also the year of the Mayan apocalypse. Several of my fellow science writers shared my delight at the utter ridiculousness of a press release making the rounds last week promoting a new pulp fictional thriller by Steve Alten: PHOBOS: Mayan Fear. That alone wouldn’t be especially noteworthy, except for its unusual physics-themed marketing ploy. Per the release:

Back in July, physicists in Geneva announced the existence of the Higgs Boson, or ‘God particle,’ a subatomic particle thought to be the key to understanding the makeup of the universe. What these physicists forgot to mention is that smashing protons together at near-light speed using the Large Hadron Collider also produces a potentially planet-ending byproduct — miniature black holes.

While CERN physicists contend that these black holes are too small to threaten the Earth, a new book just released by NY Times best-selling author Steve Alten links the Large Hadron Collider with two very real cataclysmic threats prophesied by the Mayan Calendar, with the doomsday event predicted for December 21st of this year.

According to that same press release, Alten consulted for realz with unnamed physicists, who said the outrageous scenarios described in the novel could totally happen, so there! SCIENCE! The release also included this unintentionally hilarious trailer:

Annalee Newitz of io9 has already weighed in with the appropriate degree of mocking: “I love that the author ‘consulted with physicists.’ About what? Their dinner plans? The best way to measure the fluid dynamics generated by the wind whistling between his ears?”

But I thought it would be worthwhile to provide an updated version of a couple of older Cocktail Party Physics posts addressing this whole “LHC Will Destroy the World With Mini-Black Holes” nonsense — because far from fading into historical obscurity, it keeps making the rounds of the crackpot community, most recently in a court case involving a German woman asking that the LHC be shut down. The German court tossed out her suit, but this is the second time she’s tried such a stunt.

And she’s not the first person to let unfounded fears drive her to seek legal recourse. Back in 2006, a lawsuit was filed in Hawaii’s U.S. District Court seeking a temporary restraining order against CERN and its partners in building the LHC. In this case, the plaintiffs wanted to postpone start-up preparations for “at least” four months in order to “reassess” the collider’s safety. Because, you know, it could destroy the world by creating mini-black holes. The primary plaintiff was a “former nuclear safety officer” Walter Wagner.

Don’t get me wrong. I believe very strongly that science has a responsibility to evaluate the safety of its experiments, particularly for something as massive as the LHC. LHC scientists have done so. These concerns are nothing new to anyone who has followed the development of the accelerator’s design and construction over the last 20 years. The inherent risks have been fully and fairly considered by the best scientific minds in the world, who take their responsibility for ensuring safety of operation very, very seriously. To suggest otherwise is, frankly, an insult to the world high-energy physics community.

There were not one, not two, but three safety assessments conducted prior to turning on the LHC. (“The possibility that a black hole eats up the Earth is too serious a threat to leave it as a matter of argument among crackpots,” one CERN theorist told The New York Times.) We’re talking about the most expert testimony any court could hope to have on record.

Why bring the courts into it at all? Because Wagner refused to accept the scientific consensus on the issue, that’s why. Apparently, he thought he knew better than all those world-class physicists. Hey, he studied physics and “worked on cosmic ray research” at the University of California, Berkeley , although there’s no mention of Wagner earning an actual degree, apart from a doctorate in law from the the University of Northern California in Sacramento.

In short, he knew just enough to foster panic, and not enough to make a scientifically rigorous assessment of what the true risks are. As The Daily Show made clear in a classic segment, Wagner’s notions of how probability works are hopelessly naive, to say the least:

Of course, one shouldn’t dismiss a potential risk outright. But the LHC doomsday scenario isn’t unique in modern physics history. During the Manhattan Project in the 1940s, there were concerns that a nuclear explosion would set the Earth’s atmosphere.

SLAC’s B factory caused ripples of doomsday concerns when it came online, and there were fears in the 1990s that Fermilab’s Tevatron might create a supernova instead of (or in addition to) discovering the top quark. All proved to be unfounded.

Brookhaven’s Relativistic Heavy Ion Collider (RHIC) generated all kinds of world-ending rumors when it fired up in 1999. Congress called for special hearings, and legend has it that one reporter called Brookhaven to ask whether RHIC had already created a black hole that swallowed the plane of John F. Kennedy Jr. as it flew past Long Island. (I would like to think this story is apocryphal.)

Most of the RHIC hysteria centered on strangelets: an object formed should strange quarks stick around long enough after a high-energy collision to combine with up and down quarks. If a resulting strangelet had a negative charge — an even more unlikely prospect than a strangelet forming in the first place — it would gobble up all normal matter it encountered, until the entire universe was converted into strangelets. Aiee!

Fortunately, the probability of this happening is, at best, on a par with winning the lottery more than 10 times in a row. And that’s an optimistic estimate. My favorite quote at the time was by MIT physicist Robert Jaffe, who told New York Newsday that, with regard to the formation of strangelets, it was more likely that “a spaceship is going to land in the middle of Texas, and that aliens are going to come out and tell us that the New York Yankees are all aliens.”

Mini black holes might be a wee bit more likely than the formation of strangelets. Producing a mini black hole — or a top quark, Higgs boson, or hypothetical graviton, for that matter — requires concentrating sufficient mass into very tiny spaces to reach the literally astronomical high energies needed to recreate early cosmic conditions in the lab. Even if they are produced, they wouldn’t pose a threat. Why is that? Two words: Hawking radiation.

Back in the 1990s, Stephen Hawking showed that black holes can emit tiny particles of radiation, which cause them to lose mass over time, gradually winking out of existence. It’s the result of virtual particle pairs popping out of the quantum vacuum near a black hole. Normally they would collide and annihilate into energy, but sometimes one of the pair gets sucked into the black hole, resulting in an apparent violation of energy conservation.

The mass of the black hole must decrease slightly as a result to counter this effect and ensure that energy is still conserved. How fast it evaporates depends on the black hole’s size: the smaller it is, the faster it evaporates. Ergo, even in the event the LHC produced mini black holes, they would be roughly the size of an electron, and would evaporate in mere fractions of a second.

Ultimately, the best argument against the latest “mini black holes” doomsday scenario is the same as for RHIC and its hypothetical strangelets: it hasn’t happened yet in the earth’s atmosphere, which is routinely bombarded by cosmic rays, and has been for billions of years, yet no evidence for strangelets or mini-black holes has been detected.

RHIC has been operating since 2000. The world has not yet ended. Nor did it end when Fermilab’s Tevatron turned on — not a single artificial supernova appeared, despite all the preliminary hand-wringing by fear-mongers — or when the Stanford Linear Accelerator came online. And it won’t end because of the LHC.